Katy Perry deserves better than us saying, "We told you so." But, come on, we told you so. As everyone predicted, John Mayer has apparently kicked the popster to the curb and stomped all over her heart after just two or so months of PDA-heavy togetherness.

"She's really upset about it," a source tells Us Weekly, with another adding, "She is making it seem like it wasn't serious with John, but she is hurt."

Another spy tells Radar Online that Mayer, 34, "did a real number" on Perry, 27: "She held off from his advances for the longest time, but he laid on the charm thick and promised her he was a changed man."

The twosome's connection stretches back to 2009, when they flirted up a storm one day before Perry met future ex-husband Russell Brand.

"She eventually gave in, fell head over heels for [John] and then -- yep -- once he had made his conquest, he dumped her," sighs the Radar snitch.

As we clutch our pearls in shock (shock!) at the idea of Mayer acting like a callous Casanova, the pair apparently had a chilly run-in at a mutual pal's party on Tuesday night in Los Angeles.

"Katy stayed in one room the whole night and John stayed in the other, and when they passed each other they both just kept their heads down," says a source. "It was like they had this incredible animosity for each other, and everyone else at the party could feel it. You could cut the atmosphere with a knife. It was all incredibly high school!"

That's quite a change from their behavior on Aug. 4, when they got hands-on during an afternoon pool party.

"They were all over each other in the pool and were not being shy about it," an eyewitness told us. "Katy had her legs wrapped around John in the water, and they were making out in front of everyone."

According to Us Weekly, Perry recently told friends that she was "officially dating John, not just hooking up," while another shared that she "doesn't want to get her heart broken again, but she feels a real connection and wants to see where things go."

She now joins a small but embarrassed club of ladies who have come under the spell of Mayer's seemingly hypnotic musk, alongside the likes of Jennifer Aniston, Jessica Simpson, Taylor Swift and Jennifer Love Hewitt.